The summer thermohaline structure of 2011 of the southern East China Sea shelf and its implications for the intrusion of Taiwan Warm Current and Kuroshio Current
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摘要:
利用2011年7月5个断面共30个站位的温盐深（CTD）测量资料，分析东海南部陆架水体的温盐结构和温跃层特征，探讨黑潮和台湾暖流对东海陆架水文状况的影响。结果显示，本区广泛存在着浅部温跃层和深部温跃层。浅部温跃层分布于20 m水深以内，跃层强度普遍较弱，具有明显的日内生消变化。深部温跃层分布于中、外陆架和台湾海峡。在中、外陆架的深水区，跃层底界深度约80 m，跃层厚度约10 m；跃层强度大，约为0.8 ℃/m，且较为稳定。在台湾海峡北部，温跃层分布于水深14～30 m，跃层厚度6～10 m，跃层强度偏弱，为0.2～0.5 ℃/m。在温跃层附近，由于上、下层水团温度、盐度的差异，其混合过程常出现盐指现象。在东海陆架90～110 m等深线之间，深部温跃层之下盘踞着一个深层冷水团，水温为16.8～17.6 ℃。黑潮水的入侵，使得外陆架温跃层强度减弱至0.2～0.5 ℃/m；同时，跃层层位上升，厚度加大。温跃层强度可以作为指示黑潮入侵的灵敏指标。当夏季深部温跃层强度低于0.6 ℃/m，同时伴随跃层厚度加大时，可判别为黑潮入侵。本区夏季黑潮锋可以到达110 m等深线附近。在中陆架50～80 m等深线之间，深部温跃层的消失，说明台湾暖流的强烈影响遍及整个水柱；而从南向北，台湾暖流的影响逐渐减弱。台湾海峡北部深层水温度较低，平均值为22.52 ℃，要比东海南部中陆架深层水低3 ℃，这可能意味着台湾暖流深层水主要源于黑潮分支的加入。
Abstract:Conductivity–temperature–depth (CTD) measurements along 5 transects including 30 hydrographic stations were carried out over the continental shelf of the southern East China Sea in July 2011. The thermohaline structure of waters and its characteristics are analyzed and the influence of the Kuroshio Branch Current and the Taiwan Warm Current on the hydrography of the shelf water discussed. Results show that shallow and deep thermoclines occur extensively. The former is present within 20 m in water depth, with weak gradients but apparent intraday evolution. The latter is present over the mid and outer shelf and the Taiwan Strait. The lower boundary of deep thermocline dwells at the water depth of ～80 m over the mid and outer shelf. It has a thickness of ～10 m, with stable and strong gradients of ～0.8 ℃/m. In contrast, deep thermocline dwells at the depths between 14～30 m in the northern Taiwan Strait. Its thickness usually varies between 6～10 m, with relatively weak gradients between 0.2～0.5 ℃/m. Salt fingering is observed around the deep thermocline due to the differences in temperature and salinity between the upper and lower waters. A cold water mass is observed below deep thermoclines at the isobaths between 90～110 m, with temperature between 16.8～17.6 ℃. The gradients of deep thermocline drop to 0.2～0.5 ℃/m over the outer shelf, their strata are synchronously lifted, and their thicknesses expanded, indicating the consequence of the Kuroshio intrusion. Therefore, once the deep thermocline gradient is lower than 0.6 ℃/m coupled with expanded thickness of its stratum, the Kuroshio intrusion will be distinguished. As a sensitive proxy, weakened thermocline gradients indicate that the Kuroshio front may reach up to the 110 m isobath over the outer shelf in summer. Disappearance of deep thermocline demonstrates that the Taiwan Warm Current prevails throughout the water column over the mid shelf at the isobaths between 50～80 m. Its influence reduces gradually from south to north. The deep water in the northern Taiwan Strait has a lower mean temperature of 22.52 ℃, which is 3 ℃ much lower than that of the deep water in the mid shelf of the southern East China Sea. Such a discrepancy suggests that the deep water of the Taiwan Warm Current may be derived from the inflow of the Kuroshio Branch Current.
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Key words:
- thermocline /
- Kuroshio Current /
- Taiwan Warm Current /
- Zhejiang-Fujian coastal current /
- East China Sea
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